Diffusion in Solids and Liquids IV

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Authors: Anatoly Yakovlevich Fishman, M.A. Ivanov, S.A. Petrova, Nickolai Tkachev, Vladimir Borisovich Vykhodets, Robert Grigorievich Zakharov
Abstract: Specific features of the structural phase transitions of the first order were investigated in nanosized crystals with Jahn-Teller ions. As an example the phase transitions of martensite type with changes in symmetry from a cubic to a tetragonal one have been considered. The Kanamori model was used to take into account the size of nanocrystallites and the distribution of cations over non-equivalent crystallographic sublattices in such systems. It was shown the temperature and the latent heat of the transition decrease significantly for the nanoscaled grains. A possibility of multi-phase state for nanocrystalline materials was considered.
Authors: Bin Liu, Shen Jiang, Ya Li Guo, Rachid Bennacer
Abstract: The ice-temperature storage is one of the most important methods in the preservation of fresh fruits and vegetables, while the theory about ice-temperature storage is still not mature at present. In order to study the effect of the pre-thermal processes and the post-thermal processes on the ice-temperature storage, some experiments were carried out. The experimental conditions included two different cooling rates (5°C/day and 3.5°C /day) and two different heating rates (3.2°C /day and 5.1°C/day). After the cooling, the cooled Kiwi and Pear had been stored in the ice-temperature storage for one month. During the storing time, the total sugar, the acidity and the soluble solid were measured by the national standards each two weeks. The present obtained results show that a lower cooling rate would be beneficial for sustaining hydrocarbons and increasing the acidity in fruits after ice-temperature storage; while a quicker cooling rate would increase the soluble solid in fruits after ice-temperature storage.
Authors: Ignacy Wierszyłłowski, Waldemar Niemczyk
Abstract: The paper presents results of comparative studies of tempering processes of quenched and conventionally treated tool steel vs. the same steel quenched and cryo-treated. Also ageing processes of Al-4.7%Cu alloy after conventional and cryo-treatments are analyzed and the results presented. It has been observed that in both cases cryogenic treatment has an effect on the development of the tempering and ageing processes. The mechanisms of the influence are different in each case. In the cryo-treated steel, the tempering processes already begin in the process of reaching ambient temperature from 196°C and accelerate the increase in hardness because of tempering. In conventionally treated Al-Cu alloy the processes of dissolving precipitates and the resulting decrease in hardness occur earlier than in the cryo-treated alloy. Reazons of such changes have been analyzed.
Authors: Ting Liao, Guido Roma
Abstract: The structural stability and properties of single silicon interstitials in their neutral state are investigated via ab initio methods in 3C- and 4H-SiC. By carefully checking the convergence with Brillouin Zone (BZ) sampling and supercell size we show that the split interstitial along <110> direction and tetrahedrally coordinated structure have similar formation energies in the cubic polytype. We discuss possible artifacts coming from the well known Density Functional Theory (DFT) underestimation of the band gap, which is particularly relevant for 3C-SiC. For 4H-SiC, the most energetically favorable silicon interstitial is found to be the split interstitial configuration ISisp<110> but situated in the hexagonal layer. The defect formation energies in 4H-SiC are in general larger than those in 3C-SiC, implying that the insertion of silicon interstitial introduces a large lattice distortion to the local coordination environments and affect even the second- or third-nearest neighbors. We also present an extensive comparison between well converged plane waves calculations and SIESTA [1,2] calculations based on localised orbitals basis sets.
Authors: Odila Florêncio, Paulo Sergio Silva, Rosane Ribeiro, Javier Andres Muñoz Chaves, F.H. Sá, Fábio X. Melo, Sandra G. Schneider
Abstract: Measurements of anelastic relaxation (internal friction and frequency) as a function of temperature were carried out in samples of Ti-13Nb-13Zr using two experimental apparatus: Flexural Vibration of the first tone of samples in Acoustic Elastometer System (Vibran Technology®) operating in a kilohertz bandwidth, and Torsional Vibration of the samples in Kê-type Torsion Pendulum operating in a hertz bandwidth. Experimental spectra of anelastic relaxation were determined in the temperature range from 300 K to 450 K for a heating rate of 1K/min under pressure of 10-5 Torr, in both apparatus. The results show a relaxation structure strongly dependent on the microstructure of the material. The dynamical elastic modulus (E) of Ti-13Nb-13Zr alloy can be determined by flexural vibrations by frequency (f) measurements (f  E1/2). The anelastic relaxation spectrum of Ti-13Nb-13Zr alloy was a function of temperature obtained by torsional vibrations, not revealing the presence of interstitial solutes in solid solution in the temperature range of measurements.
Authors: Ali Shokuhfar, Bahman Nasiri-Tabrizi
Abstract: Mechanical alloying and mechanochemical treatment are the major powder processing techniques on the nano scale. In these processes a high energy ball mill has been applied to synthesize compounds and nanocomposites such as aluminum metal matrix nanocomposite, hydroxyapatite and bionanocomposites based on hydroxyapatite. These processes involve deformation, cold welding, fracturing, and rewelding of powder particles. Due to the applied mechanical forces, chemical reactions and phase transformations could also take place. In the present research work, the effects of milling time, milling media, and sonication process on the microstructures and morphology of the obtained materials were evaluated by X-Ray Diffraction (XRD), Scanning Electron Microscopy (SEM), and Transmission Electron Microscopy (TEM). The results indicate that increasing the milling time leads to an increased lattice strain and decreased crystallite sizes. Furthermore, the results show that the sonication process leads to the morphological improvement of nanocrystalline hydroxyapatite. The obtained data show that the nanocrystalline hydroxyapatite with low contamination and suitable morphology can be produced in Polyamide6 vials similar to stainless steel vials, therefore it seems that using polymeric and polymeric based nanocomposite vials with high strength and wear resistance could lead to a new way for the mass production of nanocrystalline hydroxyapatite with high performance, low contamination and low cost.
Authors: Ali Shokuhfar, Bahman Nasiri-Tabrizi, Omid Gashti, Reza Ebrahimi-Kahrizsangi
Abstract: Mechanochemical process in polymeric vials has been carried out successfully to produce nanocrystalline hydroxyapatite (HAp) through two different reactions R1 and R2. Morphological properties and structural evaluation of obtained materials are studied by X-ray diffraction (XRD), scanning and transmission electron microscopy (SEM and TEM). The obtained data show that the increase in milling time leads the increasing in lattice strain and decreasing in crystallite size. The average crystallite size of HAp is below 20 and 23 nm for R1 and R2 reactions, respectively. Based on XRD patterns and SEM/TEM micrographs, the possible formation mechanism of nanocrystalline hydroxyapatite by mechanochemical process in polymeric milling media is confirmed. Final results indicate that the nanocrystalline hydroxyapatite with low chemically stable contaminations and suitable morphology can be produced in Polyamide6 vials similar to stainless steel vials, therefore it seems that using polymeric vials could lead to a new way for the mass production of nanocrystalline hydroxyapatite with high performance, low contamination and cost and also suitable morphology.
Authors: Wilhelm Eib
Abstract: The transition from elastic behaviour to plastic ow of technical materials under the inuence of increasing mechanical load is obviously of major technical importance. Nevertheless it is a challenge to formalize this transition in terms of consistent eld theories. We adopt here the beautiful theoretical work of Kröner [1], Bilby [2], and Kunin [3], who have shown how this formalization can be done. We shall go beyond their results by assuming energy dissipation if dislocations are moved through surfaces as suggested earlier [4] due to the energy density contribution from inner curved surfaces. Sometimes the mutual movement of adhering planes is described in terms of a stick-slip movement, meaning that the solid switches between elastic and plastic, possibly (and in fact in most experimental cases) showing a hysteresis between the two. Earthquake shear waves, e.g., are a dramatic example. Classical eld theories can hardly account for this eect. We shall try to describe the solid deformations as dislocations in two dierent phases, allowing for transitions between these phases. The tool is the Ginzburg-Landau-formalism in the form Haken [5] used for selforganizing quantized systems. We are aware of the fact that this procedure is consequent only after the above mentioned classical eld theories have been quantized, a still open task for theoretical physicists, but we feel that the practical benet is worth the cavalier assumptions.
Authors: Sadjad Abdi, H. Khorsand
Abstract: In recent years powder metallurgy method P/M because of complicated parts production ability is used widely, but existence of porosities in this products will decrease mechanical properties in this method, but advanced powder metallurgy methods like powder forging P/F with having profits of powder metallurgy P/M because of visible reduce in porosities will decrease powder metallurgy problems. One of the mechanical properties that is effected by the porosity is wear properties ,in this research by comparison between two groups of specimen, that first group made by powder metallurgy method that had 14% amount of porosities and second group that made by powder forge method P/F that had less than 1% amount of properties and change in wear parameters in both of groups we survey wear properties and we compare wear rate and mechanism result is showing visible relation between wear properties and amount and morphology of porosities.
Authors: Hisao Fujikawa
Abstract: The steam oxidation behavior and the oxide scale structure of Ni-based alloys containing 20 to 25 mass% Cr content were studied. The oxidation test was carried out from 550 to 700°C at 50°C intervals for 100 hours in steam. All Ni-based alloys used showed good steam oxidation resistance; higher Cr containing alloys have a little better oxidation resistance than lower Cr containing alloys. The kinetics of the oxidation rate of all Ni-based alloys used was estimated as the temperature parameter in a 100 hour test and as the temperature and time parameters, respectively. These equations could be useful for industrial applications. The oxide scale of Alloy 625 was composed of two layers. The outer layer was composed of needle-like oxides and the inner layer was composed of isometric oxides. The oxide scale was composed of Cr2O3 type. The Cr/Ni ratio in the oxide scale at 700°C was by one order larger than that at 650°C. The oxidation resistance of Ni alloys is maintained by a uniform Cr2O3 layer which is composed of high Cr content.

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